The semiconductor industry is increasingly being driven to decrease the size of semiconductor devices located on integrated circuits. For example, miniaturization is needed to accommodate the increasing density of circuits necessary for today's semiconductor products. Increased packing density and device size reduction has forced semiconductor device structures such as transistors to be located ever closer to one another.
As semiconductor device components become located closer together, the problem of so-called Joule heating becomes more pressing. In general, the bulk flow of electrons within conventional semiconductor devices results in heat that must be dissipated. The problem of Joule heating is limiting the ability of semiconductor manufacturers to produce even smaller, more compact devices. One potential option that reduces the problem of Joule heating is to utilize the spin states of electrons. Electrons have discernable spin states (e.g., up or down) that can be flipped or toggled from one state to another. The amount of energy required to flip electrons from one state to another is much smaller than the amount of energy needed for the bulk movement of charges (e.g., electrons or holes) as in current semiconductor devices. For this reason, spin-based devices offer a promising modality for very small semiconductor-based devices.
The amount of energy required to alter the electron spin may be less than the amount of energy needed for bulk charge movement (as is done in traditional semiconductor devices). For this reason, spin-based devices may offer a promising modality for very small semiconductor-based devices and provide the potential for faster logic devices, such as field-effect transistors (FETs), and may consume less power and generate less heat.
The paramount challenge to the realization of spin-based FETs is how to electronically inject spin-polarized electrons or holes into a semiconductor channel at room temperature. Spin-polarized refers to the state in which all or substantially all of the electrons are initialized to one state (e.g., all or substantially all electrons are in the spin “up” state).
One potential way to initialize electrons has to do with the electrical conductivity mismatch between ferromagnetic materials, which are metals, and semiconductor materials. In this method, electrons pass from a ferromagnetic material into a semiconductor-based material. Unfortunately, efficient spin injection based on this method cannot be achieved because of the mismatch in the density of electrons between the ferromagnetic material and the semiconductor-based material which cause electrons to randomize into different spin states when entering the semiconductor from the ferromagnetic material. Another approach that has been tried relies on quantum mechanical tunneling using an intermediate layer of silicon dioxide. Tunneling injection is, however, associated with high contact resistance. High contact resistance is, unfortunately, detrimental to FET operations. Another alternative polarization method relies on optical polarization of electrons. Optical-based polarization has proved difficult and it is generally believed to be incompatible with most microelectronic applications.
There thus is a need for a device and method that can efficiently inject spin-polarized electrons into semiconductors. The device and method should advantageously produce spin-polarized electrons of one particular state without the randomization problems associated with prior art devices and methods. In addition, such a device and method should be amendable to incorporation into current and contemplated microelectronic devices.